1. Technical Field
The present invention relates to a memory cell programming method, and particularly relates to a memory cell programming method for a rewritable non-volatile memory module, and a memory control circuit unit and a memory storage device using the same.
2. Description of Related Art
The growth of digital cameras, mobile phones, and MP3 players has been rapid in recent years. Consequently, the consumers' demand for storage media has increased tremendously. Since rewritable non-volatile memory has the advantages of being non-volatile, saving power, having a smaller volume, no mechanical structure, and quick reading/writing speed, the rewritable non-volatile memory is most suitable for portable electronic products, such as notebook computers. A solid state disk is a memory storage device using flash memory as a storage medium. For these reasons, flash memory has become a thriving part of the electronic industries.
With the improvement of the semiconductor manufacturing process, the current technology is already capable of developing flash memory modules with memory cells storing plural bits of data. Specifically, data writing (also called programming) of the flash memory module is performed by applying a voltage to a specific terminal point, such as controlling the gate voltage to change the electron quantity of a charge trapping layer in the gate, so as to change a conductive state of a channel of the memory cell to represent different storage states accordingly. For example, taking the multi-level cell (MLC) NAND flash memory as an example, when data on a lower page is 1 and data on an upper page is 1, the control circuit may control the word line control circuit not to change the gate voltage of the memory cell, but keep the storage state of the memory cell as “11.” When data on the lower page is 1, and data on the upper page is 0, the word line control circuit may, under the control of the control circuit, change the gate voltage of the memory cell to change the storage state of the memory cell into “10.” When data on the lower page data is 0 and data on the upper page is 0, the word line control circuit may, under the control the control circuit, change the gate voltage of the memory cell to change the storage state of the memory cell into “00.” When data on the lower page is 0 and data on the upper page is 1, the word line control may, under the control of the control circuit, change the gate voltage of the memory cell, so as to change the storage state of the memory cell into “01.” In other words, during data are being read, the control circuit may identify the storage state of the memory cell according to the current gate voltage of the memory cell.
Through the programming procedures, the memory cells become aged due to multiple times of injecting and removing electrons, such that a writing speed of electrons increases and the threshold voltage distribution widens. Thus, after the programming procedure is performed for multiple times, the storage state of the memory cell may not be correctly identified, and an error bit is thus generated. In addition, when the data stored in the same memory cell are read for multiple times, such as hundreds of thousands or even millions of times, it is very likely that the data are read erroneously. It is also possible that the data stored in the physical erasing unit that are read for multiple times become abnormal or missing. This phenomenon is called “read-disturb” by people having ordinary skills in the art. Particularly, the system data, such as firmware codes, file allocation table (FAT), etc., of the flash memory storage system are stored in the flash memory module, and the system data is read at a high frequency during the operation of the flash memory storage system.
Thus, how to use suitable programming parameters to program the memory cells, so as to prevent rapid degradation of the memory cells, and control the electron quantity in the charge trapping layer of the control gate in a preferable way to prevent read-disturb at the same time require the efforts of the artisans of this field.
Nothing herein should be construed as an admission of knowledge in the prior art of any portion of the present invention. Furthermore, citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention, or that any reference forms a part of the common general knowledge in the art.